chore: regenerate README (#417)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2021-05-19 04:24:56,852 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-logging-logback/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-19 04:24:58,169 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/8f4f1663-4dcd-4cf1-8b35-c5cea6ab1981/targets

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.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-logging-logback.git",
-        "sha": "ca24f7cc12796dc48efd9fef752c0f051c553236"
+        "sha": "2ff2886c11a13c223a5c7b114ccb7c7d189c41dd"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4f4b1b9b8d8b52f1e9e4a76165896debce5ab7f1"
+        "sha": "7332178a11ddddc91188dc0f25bca1ccadcaa6c6"
       }
     }
   ]

README.md

@@ -177,7 +177,7 @@ Java 11 | [![Kokoro CI][kokoro-badge-image-5]][kokoro-badge-link-5]
 
 Java is a registered trademark of Oracle and/or its affiliates.
 
-[product-docs]: https://cloud.google.com/logging/docs/setup/java/
+[product-docs]: https://cloud.google.com/logging-logback/docs/
 [javadocs]: https://googleapis.dev/java/google-cloud-logging-logback/latest/index.html
 [kokoro-badge-image-1]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-logging-logback/java7.svg
 [kokoro-badge-link-1]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-logging-logback/java7.html